A secondary battery may conventionally be sealed by housing the secondary battery inside an external member, which is comprised of a sheet-shaped member. The external member is sealed by thermal sealing along the outer peripheral edge of the external member. The secondary battery includes an electrode plate within the external member. An electrode terminal of the secondary battery is connected to the electrode plate and conducts from the outer peripheral edge of the external member.
However, because the strength of a positive electrode terminal having this kind of construction is low, a secondary battery may be damaged when housed in an electric automobile due to vibration associated with running the electric automobile. The damage may result from fractures and metal fatigue. In particular, where a group battery (battery module) is formed by connecting companion terminals of a plurality of batteries, the connected strength of the companion terminals may be reduced.